Is his Q on a relatively low cooldown because of the effect stacking? Also, just how fluid is his playstyle for far in testing?

The Q is intended to be moderate reliability. It is slightly narrower than Corki R (the little ones). Combined with the need to land two in order to get the big pay off spell, low cooldown felt appropriate. I think of it as a skill shot basic attack.

Yasuo teleports to a nearby Airborne enemy champion, briefly suspending them and all surrounding Airborne enemies mid-air as he damages them. Once he lands, Yasuo gains significant armor penetration against his enemy's bonus armor for an extended period of time.

Yasuo teleports to a nearby Airborne enemy champion, briefly suspending them and all surrounding Airborne enemies mid-air as he damages them. Once he lands, Yasuo gains significant armor penetration against his enemy's bonus armor for an extended period of time.